1. Field of the Invention
The present invention relates to an apparatus for the preparation of composite metallic or organic materials by centrifuging, a molding process using the apparatus, the composite materials obtained and the articles formed from these materials.
2. Discussion of the Related Art
The manufacture of metallic articles of revolution by centrifuging is well known. The process typically involves introducing the metallic material in the molten state into a rotating mold.
This process has also been used for a mixture consisting of a metal alloy in the liquid state and a reinforcing agent, such as graphite, a ceramic, etc. By use of this process, articles formed from a reinforced metal alloy have been obtained.
However, this process has at least two disadvantages. On the one hand, the distribution of the reinforcing agent in the manufactured article is not precisely controlled. Distribution depends essentially on the difference in density between the matrix material and the reinforcing agent. Thus, depending on the amount of this difference, the distribution of the reinforcing agent will be more or less uniform.
On the other hand, some products capable of being good reinforcing agents cannot form a stable mixture with the liquid metallic matrix material for a sufficiently long period of time; thus, the reinforcing agent separates from the metallic matrix material before it has been possible to cast the latter into the mold. This is true, for example, of copper/graphite-powder alloy mixtures. The wettability of the graphite in liquid copper alloys is very low, even when the graphite particles are coated with nickel or copper. If the graphite powder is mixed with a liquid copper alloy, the powder separates after a very short time--less than 2 seconds. It is therefore impossible, by casting such a mixture into a rotating mold, to control the distribution of the reinforcing agent in the metallic article.